W18O49 Nanofibers Functionalized with Graphene as a Selective Sensing of NO2 Gas at Room Temperature.

Recent trends in two-dimensional (2D) graphene have demonstrated significant potential for gas-sensing applications with significantly enhanced sensitivity even at room temperature. Herein, this study presents fabrication of distinctive gas sensor based on one-dimensional (1D) W18O49 nanofibers decorated 2D graphene, specifically coated on copper (Cu)-based interdigitated electrodes formed by DC sputtering, which can selectively detect NO2 gas at room temperature. The sensor device fabricated using W18O49/Gr1.5% (i.e., W18O49 nanofibers hybrid nanocomposite with 1.5 wt % graphene) displays excellent overall sensing performance at 27 °C (room temperature) with high response (∼150-160 times) to NO2 gas. The W18O49/Gr1.5%-based sensor device reflects the highly selective detection toward NO2 gas among various gases with quick response time of 3 s and speedy recovery in 6 s. The limit of detection of ∼0.3 ppm with excellent reproducibility and stability for 3 months in all weather conditions (tested in humidity conditions 20-97%) are superior features of the device under test. However, W18O49/Gr3% displayed higher selectivity for NO2 but resulted with comparatively reduced sensitivity than W18O49/Gr1.5% sensor. The enhanced sensing performance could be attributed to the graphene content to decorate the nanofibers on it, oxygen vacancies/defects, and the contacts between the sensing material and Cu. This favorable synthesis and properties of self-assembled hybrid composite materials provide a potential utilization for detecting NO2 gas in environmental safety inspection.

Towards Environment Friendly Hydrothermally Synthesized Li+, Rb+, In3+ Intercalated Phosphotungstate (PW12O40) Thin Films.

In the present investigation, a one-step hydrothermal approach is proposed to synthesize Li+, Rb+, and In3+intercalated PW12O40 (PTA) thin films. The photoelectrochemical performance of the deposited Li3PW12O40 (Li-PTA), Rb3PW12O40 (Rb-PTA), and In3PW12O40 (In-PTA) photocathodes were investigated using a two-electrode cell configuration of FTO/Li3PW12O40/(0.1 M I-/I3-)aq./Graphite. The energy band gaps of 2.24, 2.11, and 2.13 eV were observed for the Li-PTA, Rb-PTA, and In-PTA films, respectively, as a function of Li+, Rb+, and In3+. The evolution of the spinal cubic crystal structure with increased crystallite size was observed for Rb+ intercalation within the PTA Keggin structure, which was confirmed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) revealed a modification in the surface morphology from a rod-like structure to a densely packed, uniform, and interconnected microsphere to small and large-sized microspheres for Li-PTA, Rb-PTA, and In-PTA, respectively. Compositional studies confirmed that the composing elements of Li, Rb, In, P, W, and O ions are well in accordance with their arrangement for Li+, Rb+, In3+, P5+, W6+, and O2- valence states. Furthermore, the J-V performance of the deposited photocathode shows power conversion efficiencies (PCE) of 1.25%, 3.03%, and 1.62%, as a function of the incorporation of Li+, Rb+, and In3+ ions. This work offers a one-step hydrothermal approach that is a prominent way to develop Li+, Rb+, and In3+ ions intercalated PTA, i.e., Li3PW12O40, Rb3PW12O40, and In3PW12O40 photocathodes for competent solar energy harvesting.

Enhancement of CO gas sensing performance by Mn-doped porous ZnSnO3 microspheres.

This work reports the synthesis of Mn-doped ZnSnO3 microspheres (Zn1-x Mn x SnO3) using a simple co-precipitation method with (x = 0 to 0.15) and characterized for structural, morphological, surface area, and sensing properties. X-ray diffraction (XRD) analysis revealed the face-centered cubic structure of Mn-doped ZnSnO3 samples. Brunauer-Emmett-Teller (BET) analysis demonstrated the variation in surface area from 15.229 m2 g-1 to 42.999 m2 g-1 with x = 0 to 0.15 in Zn1-x Mn x SnO3. XPS indicates the change in the defect levels by Mn doping, which plays a crucial role in chemical sensors. Indeed a significant increase (≈311.37%) in CO gas sensing response was observed in the x = 0.10 sample compared to pure ZnSnO3 with a simultaneous reduction in operating temperature from 250 to 200 °C. Moreover, remarkable enhancements in response/recovery times (≈6.6/34.1 s) were obtained in the x = 0.10 sample. The Mn-doped ZnSnO3 could be a promising candidate for CO gas sensing devices used for maintaining air quality.

Terbium-Doped and Dual-Passivated γ-CsPb(I1- x Brx )3 Inorganic Perovskite Solar Cells with Improved Air Thermal Stability and High Efficiency.

Realizing photoactive and thermodynamically stable all-inorganic perovskite solar cells (PSCs) remains a challenging task within halide perovskite photovoltaic (PV) research. Here, a dual strategy for realizing efficient inorganic mixed halide perovskite PV devices based on a terbium-doped solar absorber, that is, CsPb1- x Tbx I2 Br, is reported, which undertakes a bulk and surface passivation treatment in the form of CsPb1- x Tbx I2 Br quantum dots, to maintain a photoactive γ-phase under ambient conditions and with significantly improved operational stability. Devices fabricated from these air-processed perovskite thin films exhibit an air-stable power conversion efficiency (PCE) that reaches 17.51% (small-area devices) with negligible hysteresis and maintains >90% of the initial efficiency when operating for 600 h under harsh environmental conditions, stemming from the combined effects of the dual-protection strategy. This approach is further examined within large-area PSC modules (19.8 cm2 active area) to realize 10.94% PCE and >30 days ambient stability, as well as within low-bandgap γ-CsPb0.95 Tb0.05 I2.5 Br0.5 (Eg  = 1.73 eV) materials, yielding 19.01% (18.43% certified) PCE.

Reducing Defects of All-Inorganic γ-CsPbI2Br Thin Films by Ethylammonium Bromide Additives for Efficient Perovskite Solar Cells.

Obtaining good-quality perovskite thin films is a fundamental facet that contributes to efficient inorganic perovskite solar cells. Herein, we successfully deposited ethylammonium bromide (EABr) additive-assisted high quality γ-CsPbI2Br perovskite films under ambient conditions. Detailed morphological, structural, optical, charge transport, photovoltaic performance, and stability properties have been studied. It is observed that the EABr additive helps to retard the crystal growth of perovskite films to produce a highly crystalline perovskite film with microsized grains (>1 µm) and with reduced grain boundaries. The fabricated devices based on an optimum amount of EABr (4 mg mL-1) exhibited the highest 14.47 % power conversion efficiency. Moreover, the EABr-4 mg mL-1-assisted γ-CsPbI2Br-based devices achieved a high thermal long-term stability and maintained ∼75% of their initial efficiency over 180 h at 85 °C thermal stress under ambient conditions (relative humidity: ∼35%) without encapsulation. This additive-assisted method suggests a new pathway to achieve high-quality perovskite films with a stabilized photoactive black phase and efficient devices.

Implementing Dopant-Free Hole-Transporting Layers and Metal-Incorporated CsPbI2Br for Stable All-Inorganic Perovskite Solar Cells.

Mixed-halide CsPbI2Br perovskite is promising for efficient and thermally stable all-inorganic solar cells; however, the use of conventional antisolvent methods and additives-based hole-transporting layers (HTLs) currently hampers progress. Here, we have employed hot-air-assisted perovskite deposition in ambient condition to obtain high-quality photoactive CsPbI2Br perovskite films and have extended stable device operation using metal cation doping and dopant-free hole-transporting materials. Density functional theory calculations are used to study the structural and optoelectronic properties of the CsPbI2Br perovskite when it is doped with metal cations Eu2+ and In3+. We experimentally incorporated Eu2+ and In3+ metal ions into CsPbI2Br films and applied dopant-free copper(I) thiocyanate (CuSCN) and poly(3-hexylthiophene) (P3HT)-based materials as low-cost hole transporting layers, leading to record-high power conversion efficiencies of 15.27% and 15.69%, respectively, and a retention of >95% of the initial efficiency over 1600 h at 85 °C thermal stress.

Efficient and Stable All-Inorganic Niobium-Incorporated CsPbI2Br-Based Perovskite Solar Cells.

Inorganic cesium lead halide perovskite (CsPbX3) is a promising light-harvesting material to increase the thermal stability and the device performance as compared to the organic-inorganic hybrid counterparts. However, the photoactive stability at ambient conditions is an unresolved issue. Here, we studied the influence of Nb5+ ions' incorporation in the CsPbI2Br perovskite processed at ambient conditions. Our results exhibited that 0.5% Nb-incorporated CsPb1-xNbxI2Br (herein x = 0.005) thin films show excellent uniformity and improved grain size because of the optimum concentration of Nb5+ doping and hot-air flow. The improved grain size and uniform film thickness deliver a superior interface between the CsPb1-xNbxI2Br layer and the hole-transporting material. The fabricated all-inorganic perovskite solar cell (IPVSC) devices exhibited the Nb5+ cation incorporation which enables decreased charge recombination, leading to negligible hysteresis. The champion device produces an open-circuit voltage (VOC) as high as 1.317 V. The IPVSC device containing a CsPb0.995Nb0.005I2Br composition delivers the highest power conversion efficiency of 16.45% under a 100 mW cm-2 illumination and exhibits a negligible efficiency loss over 96 h in ambient conditions.

A thiourea additive-based quadruple cation lead halide perovskite with an ultra-large grain size for efficient perovskite solar cells.

Quadruple cation-based perovskite solar cells (PVSCs) have crossed the power conversion efficiency (PCE) of 25.2% because of their effective light harvesting ability. The perovskite materials and type of additives play a crucial role in improving the photovoltaic performance and stability. Therefore, here, we demonstrated a simple approach to reduce the grain boundaries and increase the grain size by adding thiourea (TU) as an additive in mixed halide (FAPbI3)0.85(MAPbBr3)0.15, triple cation Cs0.05[(FAPbI3)0.85(MAPbBr3)0.15]0.95 and quadruple Rb0.05{Cs0.05[(FAPbI3)0.85(MAPbBr3)0.15]0.95}0.95 cation perovskite absorbers. Our results indicate that the TU-added perovskite thin films have positive effects on the grain size, which improved up to 2.6 µm for the quadruple cation. Final optimization with the quadruple cation containing TU additive-based PVSC exhibited a 20.92% PCE, which is higher than additive-free PVSCs. Furthermore, the stability of the additive-modified PVSCs is much higher than that of bare films due to their ultra-large grain size with reduced grain boundaries. In addition, our thermal stress results exhibited that the additive-based PVSC devices display better thermal stability of more than ∼100 h at 60 °C without encapsulation.

Hot-Air-Assisted Fully Air-Processed Barium Incorporated CsPbI2Br Perovskite Thin Films for Highly Efficient and Stable All-Inorganic Perovskite Solar Cells.

Replacement of conventional organic cations by thermally stable inorganic cations in perovskite solar cells (PSCs) is one of the promising approaches to make thermally stable photovoltaics. However, conventional spin-coating and solvent-engineering processes in a controlled inert atmosphere hamper the upscaling. In this study, we demonstrated a dynamic hot-air (DHA) casting process to control the morphology and stability of all-inorganic PSCs which is processed under ambient conditions and free from conventional harmful antisolvents. Furthermore, CsPbI2Br perovskite was doped with barium (Ba2+) alkaline earth metal cations (BaI2:CsPbI2Br). This DHA method facilitates the formation of uniform grain and controlled crystallization that makes stable all-inorganic PSCs which enables an intact black α-phase under ambient conditions. The DHA-processed BaI2:CsPbI2Br perovskite photovoltaics shows the champion power conversion efficiency (PCE) of 14.85% (reverse scan) for a small exposure area of 0.09 cm2 and 13.78% for a large area of 1 × 1 cm2 with excellent reproducibility. Interestingly, the hot-air-processed devices retain >92% of the initial efficiency after 300 h. This DHA method facilitates a wide processing window for upscaling the all-inorganic perovskite photovoltaics.

Quantum Dot Based Solar Cells: Role of Nanoarchitectures, Perovskite Quantum Dots, and Charge-Transporting Layers.

Quantum dot solar cells (QDSCs) are attractive technology for commercialization, owing to various advantages, such as cost effectiveness, and require relatively simple device fabrication processes. The properties of semiconductor quantum dots (QDs), such as band gap energy, optical absorption, and carrier transport, can be effectively tuned by modulating their size and shape. Two types of architectures of QDSCs have been developed: 1) photoelectric cells (PECs) fabricated from QDs sensitized on nanostructured TiO2 , and 2) photovoltaic cells fabricated from a Schottky junction and heterojunction. Different types of semiconductor QDs, such as a secondary, ternary, quaternary, and perovskite semiconductors, are used for the advancement of QDSCs. The major challenge in QDSCs is the presence of defects in QDs, which lead to recombination reactions and thereby limit the overall performance of the device. To tackle this problem, several strategies, such as the implementation of a passivation layer over the QD layer and the preparation of core-shell structures, have been developed. This review covers aspects of QDSCs that are essential to understand for further improvement in this field and their commercialization.

Synthesis of nanoporous Mo:BiVO4 thin film photoanodes using the ultrasonic spray technique for visible-light water splitting.

The use of bismuth vanadate (BiVO4) scheelite structures for converting solar energy into fuels and chemicals for fast growth in lab to industrial scale for large-area modules is a key challenge for further development. Herein, we demonstrate a new ultrasonic spray technique as a scalable and versatile coating technique for coating pristine and doped nanoporous BiVO4 thin film photoanodes directly on FTO-coated glass substrates for water splitting under visible irradiation. The successful Mo doping in BiVO4 lattice was confirmed by various characterization techniques such as XRD, Raman, EDS and XPS. The Mo:BiVO4 photoelectrode showed excellent performance with higher stability as compared to pristine BiVO4 samples.

Bio-inspired Carbon Hole Transporting Layer Derived from Aloe Vera Plant for Cost-Effective Fully Printable Mesoscopic Carbon Perovskite Solar Cells.

Herein, we introduce a new ecofriendly naturally extracted cross-linked carbon nanoparticles as a hole transporting layer (C-HTL) prepared by an ancient Indian method for carbon based printable mesoscopic perovskite solar cells (C-PSCs), which is low-cost so far used for fully printable PSCs. The fabricated PSCs having Glass/FTO/mp-TiO2/ZrO2/perovskite/AV-C configuration exhibited current density ( JSC) of 20.50 ± 0.5 mAcm-2, open circuit voltage ( VOC) of 0.965 ± 0.02 V and fill factor (FF) of 58 ± 2%, resulting in 12.3 ± 0.2% power conversion efficiency (PCE) for MAPbI3 perovskite absorber. The aloe-vera processed carbon C-HTL based PSCs yields up to 12.50% power conversion efficiency and 15.80% efficiency for conventional spiro-MeOTAD based HTM. The air and moisture stability >1000 h at >45% relative humidity (RH) for cross-linked AV-C nanoparticle-based PSCs. This stability is very high compared to conventional spiro-MeOTAD HTM-based PSCs. The prepared carbon nanoparticles facilitate an excellent penetration of perovskite absorber in triple-layer-based scaffold, which enables a high-quality perovskite crystal and results in high PCE. This novel bio-inspired AV-C cross-linked nanoparticle-based natural carbon C-HTL is low-cost until date. We believe this technique would be suitable for and helpful toward fully printable and air-moisture-stable PSCs.

Symmetric supercapacitor: Sulphurized graphene and ionic liquid.

Symmetric supercapacitor is advanced over simple supercapacitor device due to their stability over a large potential window and high energy density. Graphene is a desired candidate for supercapacitor application since it has a high surface area, good electronic conductivity and high electro chemical stability. There is a pragmatic use of ionic liquid electrolyte for supercapacitor due to its stability over a large potential window, good ionic conductivity and eco-friendly nature. For high performance supercapacitor, the interaction between ionic liquid electrolyte and graphene are crucial for better charge transportation. In respect of this, a three-dimensional (3D) nanoporous honeycomb shaped sulfur embedded graphene (S-graphene) has been synthesized by simple chemical method. Here, the fabrication of high performance symmetric supercapacitor is done by using S-graphene as an electrode and [BMIM-PF6] as an electrolyte. The particular architecture of S-graphene benefited to reduce the ion diffusion resistance, providing the large surface area for charge transportation and efficient charge storage. The S-graphene and ionic liquid-based symmetric supercapacitor device showed the large potential window of 3.2 V with high energy density 124 Wh kg-1 at 0.2 A g-1 constant applied current density. Furthermore, this device shows good cycling performance (stability) with a capacitive retention of 95% over 20,000 cycles at a higher current density of 2 A g-1.

Synthesis of SnO2 nanofibers and nanobelts electron transporting layer for efficient perovskite solar cells.

The implementation of positive alternative electron transporting layers (ETLs) with excellent electronic properties is a most promising method to up-scale low-cost highly efficient perovskite solar cell (PSC) technology. The present work demonstrates the preparation of tin oxide (SnO2) nanofibers (NF) and nanobelts (NB) as an electron transporting layer (ETL) for PSCs. The smooth and uniform nanofibers and nanobelts have been prepared using an electrospinning technique followed by calcination at 600 °C. Thermogravimetric analysis (TGA) analysis performed on the as-spun polyvinylpyrrolidone-tin oxide (PVP-SnO2) composite suggests that a calcination temperature of 600 °C is required to obtain pure SnO2 and to ensure complete removal of PVP along with other organic solvents. The structural analysis confirmed the presence of the pure tetragonal rutile phase of SnO2 nanofibers and nanobelts. The prepared nanofibers and nanobelts were further used as ETLs for PSCs. Our optimized experimental parameters yielded a JSC of 22.46 mA cm-2, a VOC of 1.081 V and FF of 66%, leading to >16% power conversion efficiency (PCE) for SnO2 nanobelts using an (FAPbI3)0.85(MAPbI3)0.15 perovskite absorber layer with good stability. The obtained PCE is much higher than that of the SnO2 NF (12.893%) morphology. Nevertheless, the synthesis of SnO2 NF/NB ETLs provides a simple, low-cost and large-scale method for PSCs.

Nanoarchitectures in dye-sensitized solar cells: metal oxides, oxide perovskites and carbon-based materials.

Dye-sensitized solar cells (DSSCs) have aroused great interest and been regarded as a potential renewable energy resource among the third-generation solar cell technologies to fulfill the 21st century global energy demand. DSSCs have notable advantages such as low cost, easy fabrication process and being eco-friendly in nature. The progress of DSSCs over the last 20 years has been nearly constant due to some limitations, like poor long-term stability, narrow absorption spectrum, charge carrier transportation and collection losses and poor charge transfer mechanism for regeneration of dye molecules. The main challenge for the scientific community is to improve the performance of DSSCs by using different approaches, like finding new electrode materials with suitable nanoarchitectures, dyes in composition with promising semiconductors and metal quantum dot fluorescent dyes, and cost-effective hole transporting materials (HTMs). This review focuses on DSSC photo-physics, which includes charge separation, effective transportation, collection and recombination processes. Different nanostructured materials, including metal oxides, oxide perovskites and carbon-based composites, have been studied for photoanodes, and counter electrodes, which are crucial to achieve DSSC devices with higher efficiency and better stability.